1. Field of the Invention
The invention relates to a filter device for extruders and injection-molding machines for the continuous processing of thermoplastic, having a screen plunger which can be displaced perpendicularly with respect to the direction of transport of the plastic, is arranged in a suction-tight manner in a housing bore and has a plurality of screen packs and vent grooves arranged in successive screen chambers.
2. Description of the Prior Art
A generic device is described in DE 29 42 849 C2. Proposed here is a continuous displacement of the screen plunger through the extruder bore in such a way that the pressure downstream of the screen plunger, i.e. downstream of the screen pack, is kept constant.
In the case of this known device, although for a short time two screen chambers and the throughflow bores following on therefrom are in use, it is not envisaged that flow is introduced into the two throughflow bores over a prolonged period.
In DE 28 36 847 A1 there is described a multi-screw extruder with a screen changing device, in which the two bores, flowing one into the other, of the two screws merge into an outlet bore in a rheologically favorable way, this outlet bore, which is of an elongate design, being fanned out into die bores. The object of this known device, and the solution achieving it, is the transition of the opening from a multi-screw extruder into an outlet opening adjoined by die openings. The transition is intended to follow a rheologically favorable path.